This invention relates to an axial flow fan for an internal combustion engine, especially for an automotive engine.
In recent years, miscellaneous instruments and accessories have been equipped with an automotive engine, so that the vacant space in an engine compartment tends to become smaller. Most of the air passing through a fan flows out of the engine compartment through gaps between body frames and cover plates of a car. On the other hand, some of the air passing through the fan turns back toward the upstream side of the fan due to a turbulent flow around the tips of the fan blades. This circulation flow or countercurrent flow grows in proportion to an increase of a tip clearance, i.e., the clearance between a periphery of a cooling fan and an inner surface of a fan shroud. This circulation flow exhibits disadvantages in that the air flow is substantially reduced and the fan efficiency drops.
In Japanese Utility Model Public Disclosure No. 71921/1981 (SHO 56-71921), the above-mentioned circulation flows are illustrated. In this invention, a flange-type extension is carried at the fan shroud so as to reduce the tip clearance and to avoid the circulation flow. However, small tip clearances tend to cause collisions between the fan blade and the fan shroud.